Hold off on placing your wagers ... money has become a big snag in George Zimmerman's boxing match against DMX -- the rapper's rep tells TMZ, contract negotiations are STILL ongoing ... so the fight isn't official ... yet.

The rep Domenick Nati tells us, DMX verbally agreed to "beat Zimmerman's ass" ... IF and when he sees the terms of a contract ... which hasn't happened yet. Once an agreement has been finalized, we're told DMX will officially be down for the bout.